The present invention relates to a coring apparatus with integrated fluid analysis capabilities for in situ analysis of core samples from a subterranean formation.
In order to analyze core samples from a subterranean formation, a core apparatus drills a core sample. Once at the surface, the core sample is often preserved by hermetically sealing the core sample in a thick coating of wax or by freezing with dry ice. The purpose of preservation is primarily to maintain the core and any fluids therein and the distribution of those fluids in the core sample as close as possible to reservoir conditions. Additionally, effective preservation prevents changes in the rock, e.g., mineral oxidation and clay dehydration.
However, as the native pressure of the core sample is invariably much higher than the pressure at the surface, the gases and light fluids that may have been trapped in the rock will escape from the core sample as it is brought to the surface thus making the core sample less accurate in providing a picture of the subterranean formation from which the core sample was taken. Determining accurate gas volumes, content and deliverability, can be important when attempting to assess the economics of an unconventional gas play, e.g., gas hydrates and shales. These determinations rely heavily on the analysis of freshly cut core. The escaped gas, in effect, leaves a data gap, which can be accounted for with a theoretical model that may or may not approximate downhole conditions.
A method known as “pressure coring” attempts to mitigate the escape of pressurized gases by encapsulating the core in a pressure vessel downhole. Once the core is cut, the core chamber is sealed at reservoir pressure to prevent gases from escaping the vessel while bringing to the surface. At surface, the gas is extruded and analyzed on-site or in a laboratory. Pressure coring, however, can be difficult to implement with increased health and safety risks. Pressure coring requires specialized training to deal with the high pressure equipment to retrieve the core sample. Further, the containers are pressurized typically to several thousand psi, which introduces the risk of explosions. Also, if high levels of toxic gases, like H2S, are collected, leaks could pose serious risks to health and life.